Method of making electric heaters



Sept. 22, 1953 A. P. CHARBONNEAU METHOD OF MAKING ELECTRIC HEATERS Filed June 7, 1947 .Il/Z

Patented Sept. 22, 1953 METHOD OF MAKING ELECTRIC HEATERS Allan P. Charbonneau, Wauwatosa, Wis., assignor to Cutler-Hammer, Inc.,

Milwaukee, Wis., a

corporation of Delaware Application June 7, 1947, Serial No. 753,326

3 Claims. (01. 29-1555) This invention relates to a method of making electric heaters, such method being especially advantageous for making heaters of the tubular sheath type.

An object of the invention is to overcome diificulties encountered in preparing heaters of the tubular sheath type for filling from one end of the sheath.

' Another object is to facilitate and expedite completion of such heaters, particularly the terminal portions thereof.

Other objects and advantages of the invention will hereinafter appear.

The accompanying drawing exemplifies certain of the ways in which therinstant method may be carried out, it being understood that the'method is not to be regarded as limited by the drawing.

In the drawing:

Figure 1 is a longitudinal view in section of a portion of a so-called tubular heater at one stage of its construction,

- Fig. 2 is a similar view showing the heater at a later stage of its construction, 7 v V I Fig. 3 is a similar view showing the heater at a still later stage of its construction, and

Fig. 4 shows at a stage in construction c'orrespending to that depicted in Fig; 1 amodified assembly.

Referring to Fig. 1 it shows at an initial stage of assembly a tubular metallic sheathf8, a heating element 9 and a plug I0. preferably relatively hard and preferably formed of polystyrene is inserted into one end ofsheath 8 with a pressed fit, substantially all of' the plug being contained within the sheath. Then the heating element shown as comprising a helical resistor I I with an end terminal I2 attached thereto in any preferred manner is inserted in the opposite end of sheath 8 and terminal I2 is inserted into a central passage I3 extending through plu Ill. The aforementioned terminal I2 is then drawn outwardly of the plug III so as to project a selected distance beyond the end of sheath 8. It may be assumed that the resistor II has at its opposite end, not shown, another terminal like terminal I2. I

The. sheath 8, after having the heating element 9 and plug I assembled therein as aforedescribed, is preferably subjected to swaging confined to that portion of the sheath surrounding plug I0. Such swaging contracts the sheath and compresses plug I 0 about the terminal I2 and is continued until the terminal is tightly gripped by the plug. The assembly at this stage is shown in Fig. 2, the end portion I4 of sheath 8 being shown Plug I0 which is idue. The assembly would then be in the state slightly deformed inwardly and the plug I0 being shown as having a tight fit with respect to terminal I2. As will be apparent the terminal I2 is now anchored in the proper position in the sheath.

It may now be assumed that the assembly shown in Fig. 2 is placed in one of the well-known types of filling machines which are adapted to A effect the filling of the sheath 8 with a suitable granular insulating material such as magnesium oxide. The assembly would be positioned in the filling machine vertically with the end containing the plug II] lowermost. The opposite end of the heating element 9 (not shown) would be suitably positioned centrally of the bore of sheath 8 and so that the opposite terminal I2 (not shown) would extend the proper distance outwardly of the corresponding end of sheath 8, the granular insulating material would be introduced into sheath 8 with intermittent compacting of the same in a well-known manner. Sheath B would be fille'd to a point below the aforementioned opposite end so as to leave an open recess therein to receive a plug like the plug I0 aforedescribed. Assuming use of such a second plug IE), it might be secured and compressed as aforedescribed.

Then it may be assumed that the assembly is subjected to well-known swaging operations over the entire length of sheath 8 to eifect further compacting of the aforementioned insulating material and to reduce the sheath 8 somewhat in cross section. ,It may further be assumed that upon. completion of the swaging operations the assembly would be placed in an annealing furnace and subjected to annealing temperatures to remove the stresses incurred in the aforementioned swaging operations and to soften the metal forming the sheath.

During the aforementioned annealing treatment the plugs II) in the ends of sheath 8 would completely volatilize and disappear, polystyrene being of such character that it will completely volatilize and disappear as gaseous combustion products at temperatures attained during annealing treatment without leaving carbon resdepicted in Fig. 3 with the sheath open at its ends to receive any preferred terminal devices to be attached to the terminals I 2 or to receive any preferred sealing material capable of withstanding hightemperatures and afiording protection of the compacted granular insulation from ingress of moisture.

Polystyrene will completely disappear as aforedescribed when heated in an inert atmosphere.

Certain preferred annealin treatments of sheath type electric heaters are carried out in inert atmospheres, such as in an atmosphere of hydrogen or illuminating gas so as to prevent oxidation of the metallic sheath.

Referring to Fig. 4, it shows an assembly comprising a tubular sheath [8, and a resistor l9 having a terminal 20, the latter projecting through a plug 2| which is inserted in one end of the sheath 18, the assembly shown being at a stage of construction corresponding to that depicted in Fig. 1.

Plug 2|, which is also preferably formed of polystyrene, is made with a greater overall length than plug i aioredescribed. It is provided with a central bore comprising a portion 22 which extends from one end of the plug inwardly a limited extent and connects with an enlarged portion 23 which extends to the opposite end of the plug. The portion 22 of the bore is of such diameter that it will just provide clearance for the terminal 26 while the portion 23 is made so that appreciable clearance is provided for terminal 20.

To produce the assembly shown in Fig. 4 plug 21 is partially inserted into the end of sheath It! with a pressed fit, the inserted end of said plug being the end with the larger diameter bore 23. Then the resistor I9 with its attached terminal 20 is inserted into the opposite end of sheath l8 and the terminal 20 is inserted into the plug to project therebeyond. Then the portion of terminal 20 immediately adjacent the outer end of plug 2| is squeezed or flattened in any preferred manner to provide a widened portion 24 such as will prevent the withdrawal of terminal 20 from the plug 2| inwardly of sheath H3.

The assembly thus effected and shown in Fig. 4 is ready for subsequent operations as aforedescribed in connection with the heater assembly depicted in Fig. 2. However it is not desirable with the modified assembly to subject sheath [8 to the special swaging operationon the end adjacent the plug 2|. As will be apparent, the enlarged portion 24 on terminal 20 provides for anchoring the lower end of the heating element 4 during filling of sheath 18. A plug like plug 2| on plug 10 may be inserted in the opposite end of sheath 18 or omitted as preferred.

The assembly after swaging and annealing would appear as depicted in Fig. 3 except in respect of the outer end of terminal 20. That portion of the terminal 20 having the widened portion 24 may be cut off so that the length of the terminal extending beyond the end of the sheath will be substantially the same as that shown in Fig. 3.

The larger bore 23 of plug 20 provides for flexure of that portion of terminal 20 which extends inwardly of sheath 8 from the juncture of the bores 23 and 22. Flexing of the terminal 20 is desirable in order that the heating element may be suitably alined within the bore of the sheath prior to the filling operation.

What I claim as new and desire to secure by Letters Patent is:

1. The method of making a sheathed electric heater wherein a resistor with a terminal end portion is surrounded by a tubular sheath containing granular refractory insulation in which said resistor is embedded and which is to be compacted by contracting said sheath, comprising inserting into an open end of said sheath prior to contracting the same a formed plug perforated to receive said terminal end portion of the resistor, said plug consisting of a material which in formed condition is compressible and which breaks down and evacuates from the sheath as vapor when subjected to heat both in air and in an inert atmosphere, then effecting anchorage in said sheath of said plug and the terminal end portion surrounded by said plug, then contracting the sheath laterally over its entire length, and then annealing the sheath to remove the stresses incurred during contraction thereof and to effect evacuation of the plug from the sheath to thereby provide a recess to accommodate a terminal end seal.

2. The method of making a sheathed electric heater, which comprises inserting a resistor with terminal end portions into a tubular sheath, then inserting into an end of said sheath a formed plug, perforated to receive a terminal end portion of said resistor, said plug consisting of a. material which in formed condition is compressible and which breaks down and evacuates from the sheath as vapor when subjected to heat both in air and in an inert atmosphere, then effecting anchorage in said sheath of said plug and the end terminal portion surrounded by said plug. then filling the sheath to a point adjacent its other end with granular insulating material, then contracting the sheath laterally over its entire length, and then annealing the sheath in an inert atmosphere to remove the stresses incurred dure ing contraction thereof and to effect evacuation of the plug from the sheath to thereby provide, a recess as for accommodation of a terminal end seal.

3. The method of making a sheathed electric heater, which comprises inserting a resistor with terminal end portions into a tubular sheath, then inserting into an end of said sheath a formed polystyrene plug perforated to receive a terminal end portion of the resistor, then effecting anchorage in said sheath of said plug and the end terminal portion surrounded by said plug, then filling the sheath to a point adjacent its other end with granular insulating material, then contracting the sheath laterally over its entire length, and then annealing the sheath to remove the stresses incurred during contraction thereof and to effect evacuation of the plug from the sheath to thereby provide a recess as for accommodation of a terminal end seal.

ALLAN P. CHARBONNEAU.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,157,916 Wentworth Oct. 26, 1915 1,494,936 Abbott May 20, 1924 1,586,897 Harris June 1, 1926 1,588,558 Thornton June 15, 1926 1,669,385 Wiegand May 8, 1928 1,767,566 Hudson June 24, 1930 1,911,063 Daly May 23, 1933 2,036,788 Abbott Apr. '7, 1936 2,130,715 Coupier Sept. 20, 1938 2,375,058 Wiegand May 1, 1945 2,413,731 Samuel Jan. 7, 1947 OTHER REFERENCES Organic Chemistry, by Norris, third ed., 1931, pp. 26, 72 and 73. Pub. by McGraw-Hill Book Co., Inc., New York, N. Y. 

